syzbot report null-ptr-deref Write in f2fs_stop_gc_thread, because
shutdown and remount can cause multi-path entry into f2fs_stop_gc_thread,
resulting in incorrect access to f2fs_gc_task before it is properly
initialized.
Reported-and-tested-by: syzbot+1a8e2b31f2ac9bd3d148@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=1a8e2b31f2ac9bd3d148
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
fs/f2fs/gc.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 6066c6eecf41..a624e8271fbc 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -27,6 +27,7 @@ static struct kmem_cache *victim_entry_slab;
static unsigned int count_bits(const unsigned long *addr,
unsigned int offset, unsigned int len);
+static DEFINE_MUTEX(gc_lock);
static int gc_thread_func(void *data)
{
@@ -203,10 +204,13 @@ int f2fs_start_gc_thread(struct f2fs_sb_info *sbi)
void f2fs_stop_gc_thread(struct f2fs_sb_info *sbi)
{
- struct f2fs_gc_kthread *gc_th = sbi->gc_thread;
+ struct f2fs_gc_kthread *gc_th;
- if (!gc_th)
+ guard(mutex)(&gc_lock);
+ gc_th = sbi->gc_thread;
+ if (!gc_th || gc_th->f2fs_gc_task < PAGE_OFFSET)
return;
+
kthread_stop(gc_th->f2fs_gc_task);
wake_up_all(&gc_th->fggc_wq);
kfree(gc_th);
--
2.43.0